Sunday, July 31, 2011

In this post, we will study a safety feature that is present in some semi-automatic pistols that are Double Action. Recall in our discussion about revolvers that double action firearms are generally able to operate in double action as well as single action mode (unless they are labelled DAO - Double Action Only, in which case they only operate in double action mode). In pistols of this sort, the user may manually pull back the hammer to cock it and then pull the trigger to release it (single action mode), or simply pull the trigger back, which cocks the hammer and then releases it (double action mode).

When fired in double action mode, the trigger pull is harder and longer since the trigger action needs to cock the hammer before releasing it.

In many cases, people like to carry their pistols with one round chambered, but the hammer decocked and any other safety devices may be turned on or off. The pistol is "considered safe" because it takes a longer and stronger trigger pull to cock and release the hammer, than if the hammer was cocked already and the trigger merely releases it.

So when a user wants to carry a pistol in this state, they initially insert a loaded magazine normally and then pull back on the pistol's slide to load the first round in the chamber. However, this same action also cocks the hammer. So, now the user wants to decock the hammer without firing the pistol. In olden days, the trick was to hold the hammer's spur down with the thumb and then pull on the trigger and then slowly let down the hammer so that it falls back to the "safe" position without discharging the loaded cartridge. Of course, this approach has some danger in that if the user's thumb slips off the hammer's spur, it could cause the hammer to strike the cartridge with force and discharge it. In order to reduce this danger, a decocking lever was introduced.

With a decocking lever, the mechanism either blocks the hammer from slamming on the firing mechanism, or by covering or retracting the firing pin out of the way, so that the hammer can be safely released without triggering the firearm. Of course, all mechanisms can fail, so it is still a good idea to point the firearm in a safe direction before operating the decocker lever.

Decocking mechanisms are found on pistols from many manufacturers: Heckler & Koch, the Sig Sauer pistol family, Walther pistols etc.

Thursday, July 28, 2011

In our last post, we studied a Glock pistol for its integrated trigger safety, but we also noted that the Glock feature two additional safeties, that guard against discharge if the firearm is accidentally dropped. We will study more about those mechanisms in this post.

Mechanisms that prevent the firearm from going off when dropped or roughly handled, fall under the class of Drop Safety. These safeties work by providing an obstruction between the firing mechanism and the cartridge and are connected to the trigger. As the trigger is being pulled, these safety devices are deactivated one after other with the trigger movement. Therefore, if the firearm is accidentally dropped, the drop safety devices are all active since no one is pulling the trigger. Hopefully they work and therefore stop the firearm from going off accidentally.

The first drop safety we will study is something we mentioned in the previous article, a firing pin block safety. This is a mechanism that sits in the path between the firing pin and the cartridge primer and prevents the firing pin from striking the cartridge, when it is active. The firing pin block is connected to the trigger and as the trigger is pulled back, the firing pin block moves out the path between the firing pin and cartridge, just before the hammer is released. The hammer then strikes the back of the firing pin and the front of the firing pin can now freely strike the base of the cartridge, since the firing pin block is now out of the way. When the trigger is released, the firing pin block moves back into place again and blocks the firing pin from striking the cartridge.

The next drop safety mechanism we will study is the hammer block. The concept is very similar to the firing pin block, except that in the case of the hammer block, the mechanism sits in between the hammer and the back of the firing pin. So when it is active, the hammer cannot strike the back of the firing pin. Like the firing pin block safety, this mechanism is also connected to the trigger and the hammer block moves out of the way as the trigger is pulled.

The next drop safety mechanism we will study is the transfer bar, which is used in revolvers. In this case, the hammer does not directly strike the cartridge. Instead, there is a transfer bar that has a firing pin attached on the other end, which contacts the cartridge. When the firearm is not in use, the transfer bar is moved out of the way between the hammer and the cartridge (which is the opposite of the other mechanisms we have seen so far.). So if the firearm is dropped accidentally and the hammer releases due to impact, the hammer still won't contact the cartridge When the trigger is pulled, the transfer bar is moved into position just before the hammer is released. The hammer now strikes the transfer bar and the other end of the transfer bar which is connected to the firing pin then strikes the cartridge and discharges the firearm.

The last drop safety mechanism we will study is the oldest one: the safety notch. Unlike all the others that we've studied so far, this is a feature that needs to be engaged by the user manually. This type is used by old revolvers, lever action rifles, some old semi-automatic pistols etc. The safety notch is a cut made to the tumbler and connected to the hammer. If it is engaged, the hammer is caught before it can strike the firing pin. Therefore, if the weapon was fully cocked and if the safety was turned on, even if an accidental drop releases the hammer, it is caught at a half-cocked point by the safety mechanism.

In many areas, the law now requires that all new firearms have at least one form of drop safety on them. Many pistols have more than one drop safety mechanism, so that if one of them is worn out, one of the others will hopefully work and prevent the pistol from accidentally discharging.

Wednesday, July 27, 2011

In our last post, we looked at Grip Safety Devices. In this post, we will look at something similar, the Integrated Trigger Safety device. This device really became popular because of Glock pistols, and other manufacturers such as Springfield Armory and Smith & Wesson also offer some models with this feature.

Public domain image. Click on image to enlarge.

The above image shows a typical Glock 17 Generation 2 pistol. If you were to click on the image to enlarge it, pay attention to the trigger assembly and notice that it seems a little thicker towards the bottom. That is because the trigger has a small spring loaded lever embedded into the lower half of the trigger. This is the integrated trigger safety device.

Similar to the grip safety, this spring loaded lever is automatically depressed by the user as a natural consequence of the user's actions, in this case, pulling the trigger. When the lever is depressed, it unlocks the main trigger and allows it to move. One cannot move the main trigger without depressing the small lever fully.

There are two additional safety devices built into Glock pistol models, which are also activated and deactivated by the trigger movement. One of these devices is a drop safety device. This guides the trigger bar in a ramp and it only releases by the rear-ward movement of the trigger. The other device is a firing pin safety, which is a small steel pin that sits in between the firing pin and the cartridge. The firing pin cannot strike the cartridge primer with the steel pin in the way. This steel firing pin safety device only drops out of the way, when the trigger is pulled. These devices get deactivated as a natural consequence of the trigger being pulled and are reactivated when the trigger is released.

Therefore, if the user were to drop the pistol accidentally, the safety devices would automatically activate and hopefully prevent the firearm from discharging. This design found widespread popularity among many users, who prefer not to move any manual lever or button to activate and deactivate the safety. The firearm still goes bang when the user pulls the trigger, but not if it were to be accidentally dropped.

Since Glock pistols became very popular, some other manufacturers took notice and used a similar feature in some of their products.

Sunday, July 24, 2011

In the last couple of posts, we studied the basics of firearm safety mechanisms as well as some manual safety mechanisms. In this post, we will study a particular type of safety mechanism called theGrip Safety. This is a popular mechanism that was first seen on the classic John Browning designed Colt M1911 pistol and later seen on other pistol models as well. It is also found in the Israeli Uzi submachine gun.

Like the name implies, a grip safety device is a lever located in the grip of the firearm. The user's hand naturally depresses the safety lever when he or she grips the firearm and this disables the safety device, thus enabling the user to pull the trigger and operate the firearm. When the user releases their grip on the firearm, the safety lever automatically pops out again and is re-enabled.

Public domain image. Click on image to enlarge.

The above image shows a Colt M1911A1 pistol. The grip safety lever is at the back of the hand grip and is automatically depressed when the user holds the pistol. There is also a manual safety lever on the firearm, at the rear of the slide, which you ought to be able to spot easily, if you've read the previous post.

Believe it or not, the original John Browning design didn't actually have a safety device, but the US Army insisted on adding a grip safety and a manual safety for the original M1911 pistol design, before they would accept it. Hence, John Browning added them for the M1911, which stayed in service from 1911-1924. The changes made to the M1911A1 model (which has been manufactured from 1924 to the present day) were relatively minor: Longer grip, wider front sight, shorter spur on the hammer etc., so it still has a grip safety and manual safety.

Public domain image. Click on image to enlarge.

The firearm depicted above is the Israeli made Uzi submachine gun. The grip safety is labelled in the above image and is pretty easy to see.

The nice thing about this design is that it is automatically enabled or disabled as the user holds or releases the firearm's grips. Therefore, a firearm with this safety device will only fire if the user is actually holding the firearm and intending to discharge it. Thus, if the user were to accidentally drop the firearm, the safety automatically enables and prevents the firearm from discharging accidentally.

In our last post, we saw some of the basic types of firearms safety mechanisms. We will now study one type, the manual or external safety.

When set to the "safe" position, such mechanisms either prevent the trigger from moving or prevent the firing mechanism from moving or disconnect the trigger from the firing mechanism (or a combination of any of the above). Since these mechanisms typically fiddle with the working of the firearm action, the levers or buttons to activate/deactivate them are typically found close to the action as well.

There are various types of these manual safeties, such as sliding lever safety, cross bolt safety (a.k.a button safety), thumb safety etc. We will look at some of these types below.

Sliding safety or Tang safety

In the above image, we see a sliding safety lever. The lever A is a rotating lever that is rotated to lock or release the barrels from the closed state. However, lever A is not the safety. If you look behind the lever A, there is a sliding switch B, which is the safety. When set to safe, the trigger cannot be pulled.

Cross bolt or Button safety

The next type of safety is typically seen in rifles and shotguns. It is a cross-bolt or button safety. The safety is the large button labelled A right behind the trigger in the image above. When the safety is activated, it prevents the trigger from moving.

Safety/Selector lever on an AK. Click on image to enlarge.

The above image shows a selector switch/safety of an AK type firearm. The long selector lever is labelled as A in the image above. When the lever is rotated to the safe position, as in the image above, it not only locks the trigger, but also physically prevents the bolt from moving backwards fully. When rotated to either the single shot or auto-fire mode, the bolt is free to move backwards all the way

Pivot Safety

The next type of safety we will look at is the Pivot safety, where the safety lever moves about a pivot point. The above particular example also falls under the class of "thumb safety". These are typically manipulated by using the thumb to manipulate the lever, hence the name. In the above image, the lever labelled A is the pivot safety. These are common on many pistols. They work by preventing the hammer from striking the firing pin and many also disengage the trigger from the rest of the action. Some of them also serve as decocking levers, i.e. the hammer may be dropped safely so that the weapon is no longer cocked. In many pistols, there is also a corresponding lever on the other side of the slide, so that the safety can be manipulated equally easily by either a left-handed or right-handed shooter.

Click on image to enlarge.

In the above example, we see another "thumb safety" type on the pistol, but this one is a sliding button type. You can see the button directly under the red dot on the slide. Like the other thumb safety we saw above, this pistol also has another button on the other side as well, so it can be used by left or right handed shooters. Actually, this pistol has two other safety mechanisms as well, a trigger safety (note the double-trigger mechanism, the first one is a trigger safety) and a grip safety as well. We will discuss these safeties in later posts.

It must be remembered that preventing the trigger from moving only is sometimes not enough to ensure safety, as a sudden blow to the firearm in the right spot can still release the firing mechanism. Hence it is better to have a mechanism that prevents the firing mechanism from moving as well.

Tuesday, July 19, 2011

In the next series of blog posts, we will look into a very important topic: firearms safety mechanisms. So what is a firearms safety mechanism and why do we need them? Well, a firearm is a weapon and we do not wish to use a firearm unless absolutely necessary, for obvious reasons. Therefore, there must be some mechanism or mechanisms that protect a firearm from accidental discharge, for example, if it were to be accidentally dropped, or if the firearm was hit by a rock or a ball or some such flying object.

The first way to do this is to carry a firearm in such a manner that it is loaded, but the user must perform an additional action before the firearm can be discharged. For example, with revolvers, people generally carry them with all but one of the chambers loaded. The lone chamber that is left unloaded is then rotated so that it is directly under the hammer and the revolver is also left uncocked. So, if the revolver were a six-shooter, the user loads five out of six chambers in the cylinder and then rotates the cylinder so that the empty chamber is the one that the revolver's hammer is directly pointing at. Therefore, if the hammer is accidentally struck, it only falls on an empty chamber. To deliberately discharge the firearm, the user needs to pull the hammer back fully with his thumb (assuming a single action revolver), which cocks the hammer and also rotates the cylinder so that the hammer will now fall on a loaded chamber. For a double action revolver, the user pulls back the trigger fully. Since it is acting in double action mode, the revolver trigger pull is much heavier and the trigger pull simultaneously cocks the hammer, rotates the cylinder to the next chamber and then releases the hammer. While this technique is actually a "policy", not a "mechanism", on many revolvers (especially older ones), this is often the only "safety mechanism" that users have.

Similarly, for modern pistols, shotguns and semi-automatic and automatic rifles, users may simply fill the magazine with cartridges and load it in, but carry the firearm without a cartridge in the firing chamber. To discharge the firearm, the user needs to hold the firearm with one hand and use the other hand to pull back on the slide (or lever in case of some shotguns or rifles) to cock the weapon and also load the first cartridge from the magazine into the firing chamber. Then the user can pull the trigger to discharge the firearm. Therefore, it takes a conscious pair of actions before the firearm is made ready to fire and it cannot be discharged unintentionally, if say, it were accidentally dropped on the hammer. This method is sometimes called the "Israeli Carry" method in the US and Canada. The origin of this term is because in the early days of the IDF (Israeli Defense Force) history, they had severe budget constraints and were forced to acquire large numbers of antiquated firearms with questionable mechanical safety mechanisms. Therefore, the early IDF personnel were taught to carry with the chamber empty and hammer down.

Of course, quite a few people like to carry their firearms loaded and cocked, with one cartridge already in the chamber (called the "+1 carry method" i.e. magazine fully loaded + 1 extra loaded in the chamber), because they do not like the idea of spending extra time to prepare the weapon for firing, which may cost one's life. Also, there may be a chance that the user may drop the weapon after they have begun firing. Obviously, there needs to be safety mechanisms to protect against these situations as well. These are the mechanical safety mechanisms we will study in the next few posts.

Safeties can be divided into two major types:

External or manual safety: These typically consist of mechanisms which explicitly require the user to switch them on or off separately. For example, there may be a safety lever or button that needs to be pushed to turn the safety mechanism off.

Internal or automatic safety: These are typically turned on or off as part of another action. For instance, many modern firearms have a hammer block that prevents the hammer from striking the firing pin. Only when the trigger is pulled is the hammer block moved out of the way of the hammer's path. Therefore, the act of pulling the trigger deactivates the internal safety and the hammer will not strike the firing pin if the firearm is accidentally dropped.

Many modern firearms come with a mixture of both types of safeties. We will look into various safety mechanisms in the next few posts.

As might be noted, the argument about carrying a firearm with the chamber loaded or not is an ongoing one. Some argue that it takes too long to load a cartridge into the chamber, while others say it doesn't take that much extra time. Others argue that in a stressful situation, one may forget to load the weapon. Also the user may not have both hands free to do this. These days, with access to better firearms, the Israelis have even stopped teaching the so-called "Israeli carry" method for the last 20 years or so. The following pair of videos shows both techniques:

Friday, July 8, 2011

In this post, we will look into a special form of sights, the Night Vision Device. These allow the user to operate in darkness and low light conditions.

The origin of night vision devices traces back to a bit before World War II broke out. The American RCA company and the German company AEG Telefunken were the pioneers in this field in the mid-1930s. The first generation of these devices (often referred to as "Generation-0") were of the "active" type. What this means is that these devices work by projecting infrared light upon a target and then making an image intensifier that is sensitive to light at these frequencies. The image intensifier uses a vacuum tube to accelerate electrons reflected from the IR beam on the target, between the anode and photo cathode of the tube. The accelerated energy charge strikes a phosphor screen (like a TV screen) where the image is focused and can be viewed via an eyepiece. Since human beings cannot see infrared light, they are unaware that they are being targeted in the dark. The first such devices were designed to be used by snipers. Many of these Gen-0 devices had pretty abysmal sensitivity and were sometimes worse than an unaided human eye. Another major problem with these devices was that the enemy troops could also wear night vision goggles and immediately detect where the sniper was hiding. The image intensifiers used vacuum tube technology and therefore, used large amounts of electricity. The use of vacuum tubes also distorted the returned images quite a lot. Vacuum tubes also had a shorter life and would often stop working in the field. The infrared illuminators were also pretty massive and often had to be mounted to a flat-bed truck. Despite these disadvantages, Gen-0 devices saw use in World War II and the Korean conflict.

The next generation devices ("Gen-1") saw action during the Vietnam War in the 1960s. Unlike Gen-0 devices, these were designed to be "passive" type devices (i.e.) they do not require their own source of infrared light and can work under moonlight conditions.

In the above image, we see a typical Generation 1 device from the Vietnam war era, mounted on top of an M16 A1 rifle. The device in question in an AN/PVS-2 Starlight scope. The device is still pretty bulky, but it doesn't need a separate IR projector. The image intensifier technology still used vacuum tube technology and still had image distortion problems. To improve the gain on these devices, multiple vacuum tubes were often cascaded together, making the image amplification to the order of 1000x to 2000x and having a service life of around 2000 hours. Despite that, these devices only worked well during full moon conditions and could not be used in anything less than half-moon conditions, which means they were pretty much useless during half the month and also on cloudy nights.

The next generation of devices ("Generation 2") came out in the 1970s. Due to major improvements in tube technology, Generation 2 devices offer much less distortion of the image and more reliability than Generation 1 devices. Gen-2 devices use microchannel plates instead of cascading vacuum tubes in the image intensifier. This makes them much more sensitive to IR light than Gen-1 devices and they can be used effectively even on moonless nights and in fog and cloudy conditions. The use of microchannel plates means that the viewed image often has a distinct square or hexagonal pattern on it. Compared to Gen-1 devices, these typically offer up to 20,000x to 30,000x amplification and last about 2500 to 4000 hours. Examples of such devices include the AN/PVS-4 and AN/PVS-5.

A soldier using an AN/PVS-4 night vision device.

Gen-2 was followed by an improved Gen-2+, which offers better performance during high and low light levels. In fact, Gen-2 devices may still be found on sale in the market today.

The next generation (Generation-3) of devices has no change in the basic technology of Generation 2 devices, but the components themselves have improved, thereby contributing to better resolution and longer life. For one thing, the photo cathode uses Gallium Arsenide (GaAs), which makes it much more efficient than the older technologies. The microchannel plate is also coated with an ion barrier film, thereby increasing the life of the device. Gen-3 devices offer 30,000x to 50,000x amplification and last about 10,000 hours or so. The first Gen-3 device was the AN/PVS-7 which was originally fielded in limited numbers in 1988 to military personnel in Fort Hood. This was followed by AN/PVS-10 and AN/PVS-14 in the 1990s and Gen-3 devices are still in use with the US military. In fact, they saw widespread use in Operation Desert Storm in the 1990s, where they certainly proved their worth.

During all this time, night vision devices were mainly used by military forces because of high prices and lack of accessibility in the civilian market. That all changed during the early 1990s, due to the collapse of the former Soviet Union. A number of Gen-0 and Gen-1 devices from Soviet military surplus became available in the western civilian market and caused an overall drop in the prices of night vision devices and they became much more accessible to civilians as well. These days, one may find Gen 2, Gen 2+ and Gen 3 devices available for sale to civilians.

Generation-4 devices are currently under development. Among the planned improvements is an automatic gated power system, which allows quick switching on and off of the photo cathode. This allows the user to move from a well lit to a dark environment or vice-versa easily.

One question that puzzles many people is why does the image of a night vision device show up in green? There is actually a very good reason for this. Apparently, the phosphor screen is deliberately coated green because it turns out that the human eye can distinguish between more shades of green than any other color.

Thursday, July 7, 2011

In our last couple of posts, we studied the topic of suppressors (a.k.a. silencers). In this post, we will study a related family of devices, the flash suppressor a.k.a flash hider. In our study of silencers, the main purpose of those is to reduce the sound level of the firearm to make it more comfortable for the user to use it. As was noted previously, many silencers also reduce the amount of flash coming out of the weapon as well.

A flash suppressor (a.k.a) flash hider is not designed to remove any sound from the firearm. Instead, its sole purpose is to reduce the flash from the muzzle. So what is muzzle flash and why do we need to get rid of it. Basically, when a firearm is fired, the cartridge propellant burns inside the barrel and pushes the bullet out. If the barrel is a little too short or if the quantity of propellant is a bit too much, some of the propellant particles end up burning outside the barrel and thereby creating a huge fireball in front of the gun. The sudden bright flash may cause the user to be temporarily blinded, especially during night time. This was not so much a problem in previous centuries, when firearms had really long barrels and propellants had plenty of time to burn completely inside the barrel. With newer powders and modern assault rifles having much shorter barrels than previous firearms, it became much more of a common occurrence. Carbines also experience this problem due to having shorter barrels than normal rifles.

A flash suppressor works in a couple of ways. First, it can redirect the exiting gases to exit via the sides of the barrel instead of in all directions, thereby keeping the shooter's vision at the top of the barrel unaffected. Second, it allows the exiting gases to expand rapidly, which cools them off and reduces their temperature, which also reduces or eliminates the brightness of the flash.

The earliest type of flash suppressor came out around World War II and is called the cone suppressor or cone flash hider. This was introduced with the Lee Enfield carbine model V. They may still be seen these days on some AK models.

A cone flash suppressor which is normally used with AKs

An AK weapon with attached cone flash hider

In the above pictures, we see a shortened AKS-74 with a cone style flash hider. It is a screw on type, which may be attached to the end of an appropriately threaded barrel. Note the hole on top in the first picture. When screwed on, this hole serves to redirect some gases up and acts as a brake to reduce the muzzle climb as well.

The next type of flash hider we will study is the duckbill type,which was often seen on early M16 models used in Vietnam. This consists of a device with a number of prongs on it, such as the image below:

As can be seen by the image above, the flattened prongs tend to resemble the bill (beak) of a duck, which gives this device its name. The prongs serve to redirect the gases to the sides, but not to the top of the barrel, so any flash that is generated will not go in that direction. While these were more effective than the earlier cone models, the prongs tended to get fouled up with vegetation when fighting in the jungle. The prongs also have a chance of getting bent on the open end, due to rough usage in the field. This doesn't mean that open-type flash hiders like this are obsolete. Some modern weapons, such as the Heckler & Koch G36 series still use them.

The problems experienced with the duckbill type flash suppressor led to the development of the birdcage type of flash suppressor. This is similar to the duckbill type, but also has a ring in front of the flash suppressor.

Birdcage type flash suppressor.

The ring in front supports the prongs and also prevents branches, grass and other vegetation from easily entering into the prongs. This type of flash suppressor came standard with the M16 A2 model. Also, in the M16A2, the flash suppressor not only prevents gas escaping from the top, the bottom is closed off as well. This prevents the hot gases from kicking up sand and dust when the shooter is firing from the prone position. This type is seen on many weapons today , including AKs, SIG, M16 etc.

Sunday, July 3, 2011

In our previous post, we studied some basics of suppressor technology. We will now study them in a bit more detail.

As we noted in the previous post, the way that suppressors work is by slowing the expanding propellant gases by trapping them in chambers and allowing them to expand and cool a bit, which causes them to escape out of the muzzle at a lower pressure and velocity than if the suppressor was not present.

There are two basic types of suppressor (a) the screw-on type (a.k.a can type or muzzle type), where a suppressor is simply screwed on to the end of the muzzle when required and (b) the integral type (a.k.a Reflex suppressor), where the suppressor is designed as part of the barrel. The screw-on type suppressor is often a third party attachment and not designed by the manufacturer of the firearm. It can be screwed-on or removed as desired by the user and can also be used on other firearms as well, provided they are all of the same or smaller caliber. Firearms typically need to be modified to add a screw thread on the outside of the barrel in order to screw on the screw-on type suppressor. Contrast this with the integral type suppressor, which is designed by the firearm manufacturer from the very beginning as part of the firearm. With this type, the barrel is enclosed by the suppressor along its length and the barrel is drilled in several places to allow the expanding propellant gases to bleed off into the enclosing suppressor. Since the integral suppressor encloses the barrel, this makes the overall weapon length shorter than if one was using a can-type suppressor.

Even though suppressors work by slowing down the exit gases, well designed ones do not affect the exit velocity of the bullet that much. In addition, many of them also reduce the flash and recoil of the firearm as well. The expanding gases do contribute to wear and tear on the internals of the suppressor. Depending on the type and materials used in constructing the device, the wear rates can greatly vary. Cheap ones can last between 15-20 shots, whereas a good one could easily last 30,000 shots or so.